Ammonium nitrate blasting explosives



Patented June 1, 1954 AMMONIUM NITRATE BLASTING EXPLOSPV ES Samuel H.Davidson, Largs, and Charles H. Rigby,

Saitcoats, Scotland,

assignors to Imperial Chemical Industries Limited, a corporation ofGreat Britain No Drawing. Application April 12, 1949, Serial No. 87,108

Claims priority, application Great Britain May 3, 1948 5 Claims.

soaked through so that the ammonium nitrate tends to be dissolved out ofthe explosive before the shot can be fired and the cartridges becomeincapable of initiation or detonation.

Moreover trouble has also been experienced in the manufacture ofammonium nitrate gelatine explosives due to a tendency of thesecompositions to stiffen on storage for short periods in ordinaryatmospheres, frequently making it difficult to extrude into cartridgeform a composition that has been allowed to stand for more than a veryshort period, so that the explosive composition must be extruded intocartridge form without delay. This is not always convenient, especiallywhen the explosive has to be transported to a separate building forextrusion.

This stiifening of ammonium nitrate gelatine explosive compositions is aresult of the absorp tion of moisture from the atmosphere by the highlyhygroscopic ammonium nitrate crystals, especially during the mixingoperation. some time has passed this moisture absorption results inneighbouring crystals of the ammonium nitrate becoming cemented togetherto a certain extent. It is a matter of common experience that inunusually damp weather the consistency of the freshly mixed gelatineexplosives tends to be unusually soft. In this case the unusually highabsorption of moisture tends to delay the onset of stiffening and thecomposition may be softer than is, desirable when it is to be extrudedinto a cartridge form, but the subsequent stiffening of the resultingcartridges may be so pronounced that they lose their deformability andcannot be pierced for the insertion of a detonator.

We have now found that these defects occasioned by the effect of wateron the ammonium nitrate in armnonium nitrate explosives can be 7minimised by the inclusion in the composition of the explosive of asmall percentage of a After Water swellable and soluble ether of amacromolecular polysaccharide. A proportion of the aforesaid etherranging from about to 5% of the weight of the explosive composition mayconveniently be included. The macro-molecular polysaccharide may be, forinstance, a water swellable and soluble ether of cellulose or starch. Itwill be understood that as the aforesaid polysaccharide ethers areoxidisable ingredients it may be advisable to omit from the carbonaceousoxidisable composition at least a portion of the usual content ofcarbonaceous ingredients or to include an increased amount of anoxidising salt in order to preserve a satisfactory oxygen balance.

The inclusion of the water swellable and soluble salts of themacro-molecular polysaccharide enables ammonium nitrate semi-gelatineand powder explosives to 'be used in wet situations where it hashitherto been customary to use the somewhat more expensive ammoniumnitrate gelatine explosives.

It would appear that when the explosive cartridge is submerged underwater that the water swellable and soluble macro-molecularpolysaccharide ether swells up in contact with the water and forms asurface protection for the interior of the explosive cartridge becauseof the low mobility of the swollen mass and the slow rate at which itinterdiffuses with the surrounding water. The interior of the cartridgethus remains satisfactorily sensitive to detonation from the time theshot has been laid until the operator is ready to fire the shot. In thecase of the ammonium nitrate gelatine explosives, the tendency of thecomposition to stiffen on storage for short periods in ordinaryatmospheres is reduced, and the tendency of the explosive to have anunduly soft consistency when freshly mixed in moist atmospheres islikewise reduced so that extrusion is facilitated.

As examples of suitable water swellable and soluble cellulose ethersthere may be used for instance a water soluble sodium salt ofcarboxymethyl cellulose, methyl cellulose, methyl ethyl cellulose orhydroxyethyl cellulose, and these may be employed in disintegratedfibrous or in powder condition. As an example of a suitable waterswellable and soluble starch ether a water soluble sodium salt ofcarboxymethyl starch may be used.

We prefer to mix the above water swellable and soluble macro-molecularpolysaccharide ether with the inorganic salts or with the othercombustibles before incorporating these with the other ingredients ofthe explosive, although We 3 may also incorporate the water swellableand soluble ether into the finished explosive with equally efficaciousresults.

By way of illustrating our invention we give the following examples inwhich the parts and proportions of ingredients are 'by weight.

Emamp le 1 70.7 parts of ammonium nitrate containing 1% of china clay,and 9.0 parts of sodium chloride are thoroughly mixed with 4 parts of awater soluble methyl cellulose of 26.4% methoxyl group content solubleand swellable in water below 50 C. The resulting mixture is thenincorporated with 10.5 parts of a nitrated 80:20 glycerine-ethyleneglycol mixture absorbed on 5.8 parts of woodmeal. The powder explosiveso obtained is tamped into waxed paper wrappers and is suitable for coalblasting.

The detonation of the cartridge can still be satisfactorily initiated bymeans of a No. 6 commercial detonator after storing it for 4 hours under6 inches of cold water even though the wrapper has been artificiallyperforated at several points.

Similarly perforated cartridges containing a composition similar to theabove except that the water soluble methyl cellulose is replaced by 2parts of woodfiour and 1 part each of additional sodium chloride andwoodmeal and thus not in accordance with the invention cannot be causedto detonate by means of a similar detonator after standing under 6inches of cold water for 15 minutes.

Example 2 70.7 parts of ammonium nitrate containing 1% of china clay and9.0 parts of sodium chloride are thoroughly mixed with 4 parts of thewater soluble sodium salt of a water soluble carboxymethyl starch. Theresulting mixture is then incorporated with a 10.5 parts of a nitrated80:20 glycerine ethylene glycol mixture absorbed on 5.8 parts ofwoodmeal. Ihe explosive powder so obtained is tamped into waxed paperwrappers, and is suitable for blasting in coal mines. The detonation ofthe cartridge can still be satisfactorily initiated, by means of a No. 6commercial detonator, after storage for 8 hours under six inches ofwater, even though the wrapper has been artificially perforated atseveral points.

Example 3 17 parts of a nitrated 80-20 glycerine-ethylene glycol mixtureand 1.8 parts of a mixture of polynitro aromatic hydrocarbons,consisting of 25% of trinitrotoluene and 75% of a mixture of isomericdinitrotoluenes that is wholly liquid at 15 C. are mixed with 0.4 partof nitrocellulose, and into the resulting jelly are incorporated 0.5part of woodmeal, 2.2 parts of comminuted oat husks, 2 parts of finelypowdered anthracite, 1 part of sulphur and 0.3 part of chalk.

The mixture so obtained is then thoroughly incorporated with a mixtureof 66 parts of ammonium nitrate containing 1% china clay, 7.8 parts ofsodium nitrate and 1 part of a finely powdered water soluble sodium saltof oarboxymethyl cellulose containing 0.7 sodium carboxymethoxy groupsper anhydroglucose unit of cellulose. The resulting moist powder istamped into waxed paper wrappers and the resulting semigelatineexplosive cartridges are suitable for quarry blasting.

Detonation of these cartridges can be satisfactorily initiated by meansof a No. 6 commercial detonator after storage under six inches of waterfor 96 hours even though the wrapper is artificially perforated atseveral points.

Similarly perforated cartridges containing a composition similar to theabove except that the water soluble sodium salt of carboxymethylcellulose is replaced by an equal weight of ammonium nitrate and thusnot in accordance with the invention cannot be caused to detonate bymeans of a similar detonator after storage for 2 hours under six inchesof water.

Example 4 26 parts of nitroglycerine and 4 parts of orthonitrotolueneare stirred with 1 part of nitrocellulose and into the resulting jellyare mixed 1 part of woodmeal, 2.5 parts of finely powderd sulphur and0.3 part of chalk.

This mixture is then incorporated for 30 minutes in a McRoberts mixerwith an intimate mixture of 47 .7 parts of ammonium nitrate, 14 parts ofsodium nitrate and 4 parts of finely powdered Water soluble sodium saltof carboxymethyl cellulose, containing 0.5 sodium carboxymethyl groupsper anhydroglucose unit. The resulting gelatine explosive is thenextruded into cartridges and wrapped with waxed paper. The explosivecartridges so obtained are suitable for blasting in quarries and mines.

The detonation of the cartridge can still be satisfactorily initiatedwith a No. 2 commercial detonator after 3 weeks storage under 10 feet ofwater, even though the cartridge has been artificially perforated atseveral points.

Similarly perforated explosive cartridges containing a compositionsimilar to the above except that the water soluble sodium salt ofcarboxymethyl cellulose is replaced by 2 parts of sodium nitrate 1 partof woodmeal and 0.5 part of starch and thus not in accordance with theinvention cannot be initiated with a No. 6 commercial detonator whenstored for three weeks under similar conditions.

Example 5 15 parts of trinitrotoluene, 71.25 parts of ammonium nitrate,and 12.75 parts of sodium chloride are initimately mixed in an Atlasmixer with 1 part of finely powdered water soluble sodium salt ofcarboxymethyl cellulose, as used in Example 3.

The powder explosive so obtained is tamped into waxed paper wrappers andthe explosive cartridges are suitable for use in fiery and dusty mines.

Artificially perforated cartridges containing this composition can stillbe fired with a No. 6 commercial detonator after storing for 8 hoursunder 6 inches of water.

Similarly perforated cartridges containing a composition similar to theabove except that the water soluble sodium salt of carboxymethylcellulose is replaced with 0.75 part of ammonium nitrate and 0.25 partof sodium chloride and thus not in accordance with the invention cannotbe initiated to detonation after storage under 6 inches of water forhour.

Example 6 15 parts of trinitrotoluene, 78.5 parts of am monium nitratecontaining 02% of parafiin wax and 2.5 parts of finely powderedaluminium are intimately mixed in an edge runner mill with 4 parts ofthe water soluble sodium salt of carboxymethyl cellulose as used in thepreceding Example 3.

The powder explosive so obtained is tamped into waxed paper Wrappers andthe explosive cartridge so obtained can still be initiated with a No. 6commercial detonator after storage under water at 25C. for 96 hours eventhough the wrapper has been artificially perforated at several points.

Similarly perforated cartridges containing a composition similar to theabove except that the water soluble sodium salt of carboxymethylcellulose is replaced by an equal weight of ammonium nitrate and thusnot in accordance with the invention cannot be initiated with a No. 6commercial detonator after storage for 3 hours under similar conditions.

Example 7 A gelatinous type of explosive composition containing ammoniumnitrate and according to the invention is produced as follows: 32.5parts of nitroglycerine, 1.8 parts of the liquid mixture of polynitroaromatic hydrocarbons as used in Example 2, 2.5 parts of Woodmeal and0.3 part of chalk are stirred with 1 part of nitrocellulose until astiff jelly is formed. This jelly is then intimately mixed with 51.5parts of ammonium nitrate, 7.4 parts of sodium nitrate and 4.0 parts offinely powdered water soluble sodium salt of carboxymethyl cellulose asused in Example 3. This composition can be compared for plasticity orsoftness using a modified type Vicat penetrometer with an otherwisesimilar mixture in which the 4.0% sodium salt of carboxyrnethylcellulose is omitted. A cord of each composition of 30 mm. length and/8" diameter is placed on end under the pin of the penetrometer whichhas been modified by fixing a fiat disc on the pin. The disc is loweredto touch the top surface of the sample under test and a reading taken. Aweight equivalent to 800 gms. is then allowed to rest on it for 60 secs.when a further scale reading is taken. The decrement in length of thecolumn of material, which has taken place under this load, calculated toa percentage of the original length is regarded as a measure of theplasticity or softness of the mixture. The temperature of the mixtureduring the tests is kept between 18 and 22 C. The results are shownbelow.

Percentage yield or degree of plasticity or softness of mixture atvarious times after mixing It will be apparent from the results of thistest that the introductiof of a proportion of water soluble sodium saltof carboxymethyl cellulose into a gelatinous type of explosivecontaining ammonium nitrate substantially retards the hardening up ofthe said explosive over short periods of storage thereby enabling thelatter to be extruded into cartridges with greater convenience.

We claim:

1. A blasting explosive composition comprising ammonium nitrate with atleast one other self-explosive sensitizing agent therefor and a smallproportion of water-swellable and soluble ether of a material selectedfrom the group consisting of cellulose and starch, said ether beinguniformly distributed throughout the composition.

2. A blasting composition as claimed in claim 1 wherein the proportionof said ether is from about 0.5 to 5% by Weight thereof.

3. A blasting explosive composition comprising ammonium nitrate with atleast one other self-explosive sensitizing agent therefor and a smallproportion of a water-sweilable and soluble ether of cellulose, saidether being uniformly distributed throughout the composition.

4. A blasting composition as claimed in claim 3 wherein the proportionof said ether is from about 0.5 to 5% by Weight thereof.

5. A blasting composition as claimed in claim 3 wherein the said etheris a water-soluble sodium salt of carboxymethyl cellulose.

References Cited in the iiie of this patent UNITED STATES PATENTS NumberName Date 1,992,217 Kirst et a1 Feb. 26, 1935 2,231,043 Winning Feb. 11,1941 2,314,809 Winning Mar. 23, 1943 2,314,832 Kirst et a1. Mar. 23,1943 2,333,367 Carey Nov. 9, 1943 2,345,582 Carey Apr. 4, 1944 2,358,384Davis Sept. 19, 1944 2,358,385 Davis et a1 Sept. 19. 1944 2,389,771Gaver Nov. 27, 1945 2,570,827 Madison et al. Oct. 9, 1951 FOREIGNPATENTS Number Country Date 359,163 Great Britain Oct. 22, 1931 OTHERREFERENCES Industrial and Engineering Chemistry, volume 37, pages943-947, October 1945.

1. A BLASTING EXPLOSIVE COMPOSITION COMPRISING AMMONIUM NITRATE WITH ATLEAST ONE OTHER SELF-EXPLOSIVE SENSITIZING AGENT THEREFOR AND A SMALLPROPORTION OF WATER-SWELLABLE AND SOLUBLE ETHER OF A MATERIAL SELECTEDFROM THE GROUP CONSISTING OF CELLULOSE AND STARCH, SAID ETHER BEINGUNIFORMLY DISTRIBUTED THROUGHOUT THE COMPOSITION.